Pian, E.E.PianFoschini, L.L.FoschiniBeckmann, V.V.BeckmannGiommi, PaoloPaoloGiommi2020-09-172020-09-172006-04-01https://hdl.handle.net/20.500.13025/440Astronomy and Astrophysics, Volume 449, Issue 2, 2006, pp.L21-L25In Spring 2005, the blazar 3C 454.3 underwent a dramatic outburst at all wavelengths from mm to X-rays. This prompted INTEGRAL observations, accomplished in 15-18 May 2005. The source was detected by the INTEGRAL instruments from 3 to 200 keV in a bright state (&tilde; 5 10<SUP>-10</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP>), at least a factor of 2-3 higher than previously observed. This is one of the brightest blazar detections achieved by INTEGRAL. During the 2.5 days of INTEGRAL monitoring, we detected a ~20% decrease in the hard X-rays (20-40 keV), indicating that we have sampled the decaying part of the flare. The decrease is less apparent in the soft X-rays (5-15 keV). The simultaneous optical variations are weakly correlated with those at soft X-rays, and not clearly correlated with those at hard X-rays. The spectral energy distribution exhibits two components, as typically seen in blazars, which can be modeled with synchrotron radiation and inverse Compton scattering occurring in a region external to the broad line region.galaxies activeX-rays observations10.1051/0004-6361 200600017http://adsabs.harvard.edu/abs/2006A&A...449L..21P2006A&A...449L..21P